1. Field of Invention
The present invention relates to a digital image composition method, and more particularly, to a digital image composition method adapted to eliminate a ghost image produced by a digital image-capturing apparatus during shooting.
2. Related Art
Nowadays, with the rapid development of digital cameras, many people choose to record memorable moments by taking photographs. However, no matter in the case of a film camera or a digital camera, blurred images are often produced due to unstable holding of the camera by a user during shooting. As long as the camera is held by bare hands, the shaking problem exists, more or less. The difference is that the hand-holding stability varies among different people, and an involuntary displacement of the camera occurs at the moment the shutter is pressed. Therefore, in order to avoid generating blurred images due to handshakes, digital camera manufacturers employ hardware to prevent the handshakes or software to correct the already blurred digital images.
Thereby, products of each digital camera manufacturer are provided with anti-handshake mechanisms different from others. The anti-handshake mechanisms are capable of detecting and suppressing image blurring phenomena caused by handshakes during shooting. The anti-handshake techniques are mainly realized by hardware or software.
As for hardware, a photosensitive element anti-handshake mode and a mechanical anti-handshake mode are generally adopted. The photosensitive element anti-handshake mode is used for increasing ISO (International Standards Organization, briefly referred to as ISO). Basically, increasing ISO merely allows the shutter to finish the action before any shaking is felt. However, increasing ISO also brings about more noises. The mechanical anti-handshake mode is to configure a motion detecting element in the digital camera. On detecting a handshake, the digital camera moves its lens in a direction opposite to that of the handshake so as to compensate the image blurring caused by displacement. Another anti-handshake method is to enlarge the aperture for increasing the amount of the incident light so as to shorten a shutter time. However, the size of the aperture depends on a combined architecture of the lens set. Generally speaking, a camera lens of a large aperture is high in cost and large in volume, and is thus difficult to be configured in consumer digital cameras.
Another mode is to compose a plurality of digital images. Although a better visual effect can be achieved, a ghost image is prone to be produced during the image composition. The reason is that a subject to be shot is not at a fixed position when two digital images are captured, so the same subject appears at different positions when the two digital images are directly composed. Referring to FIG. 1, a schematic view of a conventional composition method is shown. In FIG. 1, the top left picture is a digital image 110 captured at a first time, and the bottom left picture is a digital image 120 captured at a second time. If the two digital images are directly composed, a ghost image with the same subject appearing at different positions is shown in the right picture (digital image 130) of FIG. 1.